This invention relates generally to coherent adaptive optical systems and more particularly to such systems wherein a first electro-magnetic beam measures phase characteristics or optical path differences of a propagation path and said measured characteristics are used to compensate a second electro-magnetic beam.
My U.S. Pat. No. 3,731,103 discloses a laser system wherein adaptive phase control is used to establish an in-phase condition for transmitted energy at a remotely located target. In accordance with one embodiment of the invention of said patent, a plurality of subaperture areas of the transmitted beam are phase modulated at distinctive modulation (tagging or dither) frequencies. Due to interaction of the energy from the various subapertures, amplitude modulation components at the tagging frequencies in the received energy are indicative of phase distortions across the beam. The system adjusts the relative phase of the subaperture transmission channels to minimize the modulation components in the received energy and thereby establishes an in-phase condition, at the target, of the energy across the transmitted beam.
The adaptive array system disclosed in my U.S. Pat. No. 3,764,213 spatially modulates a received beam by phase modulating subaperture segments of the received beam at respective modulation (tagging) frequencies. The resultant signal is applied through the aperture of an image stop structure to a detector and the detector's output contains modulation components at the tagging frequencies of the respective subapertures. The degree of modulation at a given tagging frequency is indicative of the phase imbalance associated with the respective subaperture channel. By adjusting the relative phasing of the subaperture receiving channels so as to minimize the amplitude modulation components in the detector's output signal, the received beam is adjusted to approach an in-phase condition. The phase adjustment of the subaperture channels, which is set during the received portion of the operation of the system, is held during a subsequent transmission period. In this manner, the transmission beam which time shares the subaperture channels with the receiving beam is compensated so as to deliver in-phase energy to the target.
The subject invention builds upon the technology of my two cited patents so as to produce a new and useful dual-wavelength system that provides the hereinbelow set forth benefits and advantages.